The present invention relates to a polymerizable liquid crystal compound having an amido bond between two cyclic groups. The invention also relates to an optically anisotropic element prepared from the compound.
Alignment of molecules of a polymerizable liquid crystal compound can be fixed by polymerization after the molecules are aligned. The polymerizable liquid crystal compounds are described in U.S. Pat. Nos. 4,683,327, 4,983,479, 5,622,648 and 5,770,107; and W.O. Patent Nos. 95/22586 and 97/00600.
An optically anisotropic polymer prepared by the polymerization can be used as an optically anisotropic element. For example, a polarizing prism made of the optically anisotropic polymer is described in European Patent No. 428213. Further, an optical compensatory sheet (for liquid crystal display of STN mode) made of the optically anisotropic polymer is described in European Patent No. 428881. Furthermore, a cholesteric polarizer made of the optically anisotropic polymer is described in European Patent No. 606940.
The present inventors have studied polymerizable liquid crystal compounds, and have found that the known compounds have disadvantages in phase transition temperature and optical characteristics. For example, the known compounds often change into isotropic liquid at low temperatures or exhibit liquid phase within narrow temperature ranges. Further, known polymerizable liquid crystal compounds sometimes have small birefringent indexes to be used in an optically anisotropic material (such as an optically anisotropic element).
An object of the present invention is to provide a polymerizable liquid crystal compound having an appropriate phase transition temperature.
Another object of the invention is to provide a polymerizable liquid crystal compound having a large birefringent index.
A further object of the invention is to provide an optically anisotropic element having optical anisotropy, which can be easily produced.
The present invention provides a polymerizable liquid crystal compound represented by the formula (I):
Q1xe2x80x94L1xe2x80x94Cy1xe2x80x94(CHxe2x95x90CH)nxe2x80x94COxe2x80x94NR1xe2x80x94Cy2xe2x80x94L2xe2x80x94Q2xe2x80x83xe2x80x83(I)
in which each of Q1 and Q2 independently is a polymerizable group; each of L1 and L2 independently is a divalent linking group; each of Cy1 and Cy2 independently is a divalent cyclic group; R1 is hydrogen or an alkyl group having 1 to 7 carbon atoms; and n is 0 or 1.
The invention also provides An optically anisotropic element comprising a transparent support and a liquid crystal layer formed by polymerization of a polymerizable liquid crystal compound, wherein the polymerizable liquid crystal compound is represented by the formula (I).
The present inventors have found that the polymerizable liquid crystal compound represented by the formula (I) changes into isotropic liquid at a high temperature and exhibits liquid phase within a wide temperature range. Further, the compound has a large birefringent index. The compound of the formula (I) has a specific mesogen structure, in which an amide bond (xe2x80x94COxe2x80x94NRxe2x80x94) is present between two cyclic groups (Cy1 and Cy2), each of which further links to a polymerizable group (Q) through a linking group (L). Because of the specific mesogen structure, the compound can exhibit liquid phase within a wide temperature range and has a large birefringent index.
Since the polymerizable liquid crystal compound gives liquid phase within a wide temperature range, alignment of the liquid crystal molecules can be easily maintained during polymerization reaction. Accordingly, an optically anisotropic element can be easily prepared by polymerization reaction of the polymerizable liquid crystal compound represented by the formula (I).
Since the compound of the formula (I) has a large birefringent index, an optically anisotropic element having high anisotropy can be obtained.
The polymerizable liquid crystal compound of the invention is represented by the formula (I).
Q1xe2x80x94L1xe2x80x94Cy1xe2x80x94(CHxe2x95x90CH)nxe2x80x94COxe2x80x94NR1xe2x80x94Cy2xe2x80x94L2xe2x80x94Q2.xe2x80x83xe2x80x83(I)
In the formula (I), each of Q1 and Q2 independently is a polymerizable group. The polymerizable group is preferably polymerized by addition (including ring-opening) or condensation polymerization reaction. In other words, the polymerizable group is preferably a functional group which can be subjected to addition or condensation polymerization reaction.
Examples of the polymerizable groups (Q) are shown below. 
The polymerizable group (Q1 or Q2) preferably is an unsaturated polymerizable group (Q-1 to Q-7), an epoxy group (Q-8) or an aziridinyl group (Q-9), more preferably is an unsaturated polymerizable group, and most preferably is an ethylenically unsaturated group (Q-1 to Q-6).
In the formula (I), each of L1 and L2 independently is a divalent linking group. The divalent linking group is preferably selected from the group consisting of xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94NR2xe2x80x94, a divalent chain group, a divalent cyclic group and a combination thereof. R2 is hydrogen or an alkyl group having 1 to 7 carbon atoms.
Examples of the combined divalent linking group are shown below. In the examples, the left side is attached to Q (Q1 or Q2), and the right side is attached to Cy (Cy1 or Cy2). CH means a divalent chain group, and CY means a divalent cyclic group.
L1: xe2x80x94COxe2x80x94Oxe2x80x94CHxe2x80x94Oxe2x80x94
L2: xe2x80x94COxe2x80x94Oxe2x80x94CHxe2x80x94Oxe2x80x94CYxe2x80x94COxe2x80x94Oxe2x80x94
L3: xe2x80x94COxe2x80x94Oxe2x80x94CHxe2x80x94Oxe2x80x94CYxe2x80x94Oxe2x80x94COxe2x80x94
L4: xe2x80x94COxe2x80x94Oxe2x80x94CHxe2x80x94Oxe2x80x94CYxe2x80x94CHxe2x80x94
L5: xe2x80x94COxe2x80x94Oxe2x80x94CHxe2x80x94Oxe2x80x94CYxe2x80x94
L6: xe2x80x94COxe2x80x94Oxe2x80x94CHxe2x80x94Oxe2x80x94CYxe2x80x94CHxe2x80x94COxe2x80x94Oxe2x80x94
L7: xe2x80x94COxe2x80x94Oxe2x80x94CHxe2x80x94Oxe2x80x94CYxe2x80x94Oxe2x80x94COxe2x80x94CHxe2x80x94
The divalent chain groups (CH) include an alkylene group, a substituted alkylene group, an alkenylene group, a substituted alkenylene group, an alkynylene group or a substituted alkynylene group. An alkylene group, a substituted alkylene group, an alkenylene group and a substituted alkenylene group are preferred, and an alkylene group and an alkenylene group are more preferred.
The alkylene group may have a branched structure. The alkylene group preferably has 1 to 12 carbon atoms, more preferably has 2 to 10 carbon atoms, and most preferably has 3 to 8 carbon atoms.
The alkylene moiety of the substituted alkylene group is the same as the above-described alkylene group. Examples of the substituent groups of the substituted alkylene groups include a halogen atom.
The alkenylene group may have a branched structure. The alkenylene group preferably has 2 to 12 carbon atoms, more preferably has 2 to 8 carbon atoms, and most preferably has 2 to 4 carbon atoms.
The alkenylene moiety of the substituted alkenylene group is the same as the above-described alkenylene group. Examples of the substituent groups of the substituted alkylene groups include a halogen atom.
The alkynylene group may have a branched structure. The alkynylene group preferably has 2 to 12 carbon atoms, more preferably has 2 to 8 carbon atoms, and most preferably has 2 to 4 carbon atoms.
The alkynylene moiety of the substituted alkynylene group is the same as the above described alkynylene group. Examples of the substituent groups of the substituted alkylene groups include a halogen atom.
The definition and the examples of the divalent cyclic groups (CY) are the same as those for Cy1 and Cy2 described below.
R2 preferably is hydrogen or an alkyl group having 1 to 4 carbon atoms, more preferably is hydrogen or an alkyl group having 1 or 2 carbon atoms, and most preferably is hydrogen.
L2 is preferably xe2x80x94Oxe2x80x94COxe2x80x94(CHxe2x95x90CH)mxe2x80x94Cy3xe2x80x94L3xe2x80x94 or xe2x80x94(CHxe2x95x90CH)mxe2x80x94COxe2x80x94Oxe2x80x94Cy3xe2x80x94L3xe2x80x94, in which m is 0 or 3, Cy3 is a divalent cyclic group and L3 is a divalent linking group.
The above m is preferably 0 rather than 1.
The definition and the examples of the divalent cyclic group are the same as those for Cy1 and Cy2 described below.
L3 preferably is a divalent linking group selected from the group consisting of xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94NR2xe2x80x94, a divalent chain group and a combination thereof. R2 is hydrogen or an alkyl group having 1 to 7 carbon atoms. R2 preferably is hydrogen or an alkyl group having 1 to 4 carbon atoms, more preferably is hydrogen or an alkyl group having 1 or 2 carbon atoms, and most preferably is hydrogen.
L3 most preferably is xe2x80x94Oxe2x80x94CHxe2x80x94Oxe2x80x94COxe2x80x94, in which CH is a divalent chain group.
The polymerizable liquid crystal compound represented by the formula (I) preferably have three divalent cyclic groups (Cy1, Cy2 and Cy3).
In the formula (I), each of Cy1 and Cy2 independently is a divalent cyclic group.
The ring in the cyclic group preferably is a five-membered, six-membered or seven membered ring, more preferably is a five-membered or six-membered ring, and most preferably is a six-membered ring.
The ring can be condensed with another ring. However, a monocyclic ring is preferred to a condensed ring.
The ring in the cyclic group can be an aromatic ring, an aliphatic ring or a heterocyclic ring.
Examples of the aromatic rings include benzene ring and naphthalene ring. Examples of the aliphatic ring include cyclohexane ring. Examples of the heterocyclic ring include pyridine ring and pyrimidine ring.
A preferred cyclic group having a benzene ring is 1,4-phenylene. A preferred cyclic groups having a naphthalene ring include naphthalene-1,5-diyl and naphthalene-2,6-diyl. A preferred cyclic group having a cyclohexane ring is 1,4-cyclohexylene. A preferred cyclic group having a pyridine ring is pyridine-2,5-diyl. A preferred cyclic group having a pyrimidine ring is pyrimidine-2,5-diyl.
The cyclic group most preferably is 1,4-phenylene or 1,4-cyclohexylene.
The cyclic group can have a substituent group. Examples of the substituent group include a halogen atom, cyano, nitro, an alkyl group having 1 to 5 carbon atoms, a halogen-substituted alkyl group having 1 to 5 carbon atoms, an alkoxy group having 1 to 5 carbon atoms, an alkylthio group having 1 to 5 carbon atoms, an acyl group having 1 to 5 carbon atoms, an acyloxy group having 2 to 6 carbon atoms, an alkoxycarbonyl group having 2 to 6 carbon atoms, carbamoyl, an alkyl carbamoyl group having 2 to 6 carbon atoms and an amido group having 2 to 6 carbon atoms.
In the formula (I), R1 is hydrogen or an alkyl group having 1 to 7 carbon atoms. R1 preferably is hydrogen or an alkyl group having 1 to 4 carbon atoms, more preferably is hydrogen or an alkyl group having 1 to 2 carbon atoms, and most preferably is hydrogen.
In the formula (I), n is an integer of 0 or 1. Preferably, n is 0 rather than 1.
The polymerizable liquid crystal compound is preferably represented by the formula (IIa) or (IIb). The compound of the formula (IIa) is more preferred.
Q1xe2x80x94L1xe2x80x94Cy1xe2x80x94(CHxe2x95x90CH)nxe2x80x94COxe2x80x94NR1xe2x80x94Cy2xe2x80x94Oxe2x80x94COxe2x80x94(CHxe2x95x90CH)mxe2x80x94Cy3xe2x80x94L3xe2x80x94Q2xe2x80x83xe2x80x83(IIa)
Q1xe2x80x94L1xe2x80x94Cy1xe2x80x94(CHxe2x95x90CH)nxe2x80x94COxe2x80x94NR1xe2x80x94Cy2xe2x80x94(CHxe2x95x90CH)mxe2x80x94COxe2x80x94Oxe2x80x94Cy3xe2x80x94L3xe2x80x94Q2xe2x80x83xe2x80x83(IIb)
In the formulas (IIa) and (IIb), each of Q1 and Q2 independently is a polymerizable group. The definition and the examples of the polymerizable group are the same as those described for the formula (I).
In the formulas (IIa) and (IIb), each of L1 and L3 independently is a divalent linking group. The divalent linking group is preferably selected from the group consisting of xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94COxe2x80x94, xe2x80x94NR2xe2x80x94, a divalent chain group and a combination thereof. R2 is hydrogen or an alkyl group having 1 to 7 carbon atoms. R2 preferably is hydrogen or an alkyl group having 1 to 4 carbon atoms, more preferably is hydrogen or an alkyl group having 1 or 2 carbon atoms, and most preferably is hydrogen.
L1 preferably is xe2x80x94COxe2x80x94Oxe2x80x94CHxe2x80x94Oxe2x80x94, in which CH is a divalent chain group. L3 preferably is xe2x80x94Oxe2x80x94CHxe2x80x94Oxe2x80x94COxe2x80x94, in which CH is a divalent chain group.
The definition and the examples of the divalent chain group (CH) are the same as those described for the formula (I).
In the formulas (IIa) and (IIb), each of Cy1, Cy2 and Cy3 independently is a divalent cyclic group.
The definition and the examples of the divalent cyclic group are the same as those described for the formula (I).
In the formulas (IIa) and (IIb), R1 is hydrogen or an alkyl group having 1 to 7 carbon atoms. R1 preferably is hydrogen or an alkyl group having 1 to 4 carbon atoms, more preferably is hydrogen or an alkyl group having 1 or 2 carbon atoms, and most preferably is hydrogen.
In the formulas (IIa) and (IIb), each of m and n is independently an integer of 0 or 1. Preferably, each of m and n is 0 rather than 1.
The polymerizable liquid crystal compound is further preferably represented by the formula (IIIa) or (IIIb). The compound of the formula (IIIa) is furthermore preferred. 
In the formulas (IIIa) and (IIIb), each of Q1 and Q2 independently is a polymerizable group. The definition and the examples of the polymerizable group are the same as those described for the formula (I).
In the formulas (IIIa) and (IIIb), each of L1 and L3 independently is a divalent linking group. The divalent linking group is preferably selected from the group consisting of xe2x80x94Oxe2x80x94, xe2x80x94Sxe2x80x94, xe2x80x94COxe2x80x94, NR2xe2x80x94, a divalent chain group and a combination thereof. R2 is hydrogen or an alkyl group having 1 to 7 carbon atoms. R2 preferably is hydrogen or an alkyl group having 1 to 4 carbon atoms, more preferably is hydrogen or an alkyl group having 1 or 2 carbon atoms, and most preferably is hydrogen.
L1 preferably is xe2x80x94COxe2x80x94Oxe2x80x94CHxe2x80x94Oxe2x80x94, in which CH is a divalent chain group. L3 preferably is xe2x80x94Oxe2x80x94CHxe2x80x94Oxe2x80x94COxe2x80x94, in which CH is a divalent chain group.
The definition and the examples of the divalent chain group (CH) are the same as those described for the formula (I).
In the formulas (IIIa) and (IIIb), each of m and n is independently an integer of 0 or 1. Preferably, each of m and n is 0 rather than 1.
In the formulas (IIIa) and (IIIb), the benzene rings A and B can have substituent groups. Examples of the substituent group are the same as those of the divalent cyclic group in the formula (I).
Examples of the polymerizable liquid crystal compounds represented by the formula (I) are shown below. 
The polymerizable liquid crystal compound represented by the formula (I) can be synthesized by referring known methods (for example, described in Methoden der Organischen Chemie [Houben-Weyl], Some Specific Methods [Thieme-Verlag, Stuttgart], Jikken Kagaku Koza and Shin-Jikken Kagaku Koza). The compounds can also be synthesized by referring to the descriptions of U.S. Pat. Nos. 4,683,327, 4,983,479, 5,622,648 and 5,770,107; W.O. Patent Nos. 95/22586, 97/00600 and 98/47979; and British Patent No. 2297549.
[Optically Anisotropic Element]
An optically anisotropic element can be prepared by coating an orientation layer with a liquid crystal composition (coating solution) comprising the polymerizable liquid crystal compound represented by the formula (I) and then polymerizing the molecules of the liquid crystal compound to form a liquid crystal layer.
The composition can be applied according to a conventional coating method such as an extrusion coating method, a direct gravure coating method, a reverse gravure coating method, a die coating method or a bar coating method.
The liquid crystal molecules are fixed with the alignment maintained. The liquid crystal molecules are fixed by a polymerization reaction of the polymerizable groups (Q) in the molecules. The polymerization reaction can be classified into a thermal reaction using a thermal polymerization initiator and a photo reaction using a photo polymerization initiator. A photo polymerization reaction is preferred.
Examples of the photo polymerization initiators include xcex1-carbonyl compounds (described in U.S. Pat. Nos. 2,367,661, 2,367,670), acyloin ethers (described in U.S. Pat. No. 2,448,828), xcex1-hydrocarbon substituted acyloin compounds (described in U.S. Pat. No. 2,722,512), polycyclic quinone compounds (described in U.S. Pat. Nos. 2,951,758, 3,046,127), combinations of triarylimidazoles and p-aminophenyl ketones (described in U.S. Pat. No. 3,549,367), acridine or phenazine compounds (described in Japanese Patent Provisional Publication No. 60(1985)-105667 and U.S. Pat. No. 4,239,850) and oxadiazole compounds (described in U.S. Pat. No. 4,212,970).
The amount of the photo polymerization initiator is preferably in the range of 0.01 to 20 wt. %, and more preferably in the range of 0.5 to 5 wt. % based on the solid content of the coating solution.
The light irradiation for the photo polymerization may be conducted with an ultraviolet ray.
The exposure energy is preferably in the range of 20 to 50,000 mJ/cm2, and more preferably in the range of 100 to 800 mJ/cm2. The light irradiation can be conducted with the layer heated to accelerate the photo polymerization reaction.
The liquid crystal layer has a thickness preferably in the range of 0.1 to 50 xcexcm, more preferably 1 to 30 xcexcm, and most preferably in the range of 5 to 20 xcexcm.
[Orientation Layer]
The orientation layer can be formed by rubbing treatment of an organic compound (preferably a polymer), oblique evaporation of an inorganic compound, formation of a micro groove layer, or stimulation of an organic compound (e.g., (xcfx89-tricosanoic acid, dioctadecylmethylammonium chloride, methyl stearate) according to a Langmuir-Blodgett method. Further, the aligning function of the orientation layer can be activated by applying an electric or magnetic field to the layer or irradiating the layer with light. The orientation layer is preferably formed by rubbing a polymer. The rubbing treatment can be conducted by rubbing a layer containing the aforementioned polymer with paper or cloth several times along a certain direction.
The polymer used for the orientation layer is selected according to aimed alignment (particularly, aimed average inclined angle) of the liquid crystal molecules.
For horizontally aligning the liquid crystal molecules (at an average inclined angle of 0 to 50xc2x0), a polymer that does not reduce the surface energy of the orientation layer (i.e., a polymer usually used for an orientation layer) is used.
In contrast, for vertically aligning the liquid crystal molecules (at an average inclined angle of 50 to 90xc2x0), a polymer that reduces the surface energy of the orientation layer is used. That polymer preferably has a hydrocarbon group of 10 to 100 carbon atoms at the side chain.
Concrete examples of the polymer are described in various publications concerning liquid crystal cells or optical compensatory sheets.
The orientation layer has a thickness of preferably 0.01 to 5 xcexcm, more preferably 0.05 to 1 xcexcm.
After the liquid crystal molecules are aligned with the orientation layer, the liquid crystal layer can be transferred onto the transparent support. The aligned and fixed liquid crystal molecules can keep the alignment without the orientation layer.
For aligning the molecules at an average inclined angle less than 5xc2x0, neither rubbing treatment nor the orientation layer is needed. However, an orientation layer (described in Japanese Patent Provisional Publication No. 9(1997)-152509) that forms chemical bonding at the interface between the liquid crystal molecules and the layer may be provided to improve the adhesion. In that case, rubbing treatment is unnecessary.
[Transparent Support]
A transparent support is a glass plate or a polymer film, preferably a polymer film. The term xe2x80x9ctransparentxe2x80x9d here means that light transmittance is not less than 80%.
The transparent support has a thickness preferably in the range of 10 to 500 xcexcm, and more preferably in the range of 50 to 200 xcexcm.
The transparent support can be subjected to a surface treatment (e.g., glow discharge treatment, corona discharge treatment, ultraviolet (UV) treatment, flame treatment) to improve adhesion to a layer formed on the support (e.g., adhesive layer, orientation layer, liquid crystal layer).
An ultraviolet absorber may be incorporated in the transparent support.
An adhesive layer (undercoating layer) can be provided on the transparent support. Japanese Patent Provisional Publication 7(1995)-333433 describes the adhesive layer. The thickness of the adhesive layer is in the range of preferably 0.1 to 2 xcexcm, more preferably 0.2 to 1 xcexcm.
[Use of Optically Anisotropic Element]
The optically anisotropic element of the invention can be used as an optical compensatory sheet for liquid crystal displays of various modes. Examples of the display modes include TN (twisted nematic) mode, IPS (in-plane switching) mode, FLC (ferroelectric liquid crystal) mode, OCB (optically compensatory bend) mode, STN (super twisted nematic) mode, VA (vertically aligned) mode, GH (guest-host) mode and HAN (hybrid aligned nematic) mode.
The optically anisotropic element can be also used as a polarizing prism (described in European Patent No. 428213).
Further, the element can be used as a cholesteric polarizer (described in European Patent No. 606940).